For many industrial purposes, it is desirable to accurately measure the flow of liquid. For example, many industrial coatings are formed from mixing a resin and a hardener just prior to application. When applying a coating composed of a two component mixture, it is desirable to accurately measure liquid flow to maintain an accurate mixing ratio. The coating quality may be significantly affected by relatively small deviations in the mixing ratio. For many industrial applications a positive displacement flow meter is used to measure liquid flow.
A typical positive displacement flow meter consists of two meshed gears mounted to rotate in overlapping cylinders formed in a housing. Liquid enters an inlet chamber formed between the cylinder walls and the teeth on the two gears on one side of the location where the gear teeth mesh. The gears are rotated by the fluid flow until the fluid trapped between the teeth and the cylinder walls enters an outlet chamber on the opposite side of the location where the gear teeth mesh. Each time the gears rotate through an increment equal to the spacing between two adjacent gear teeth, a volume of liquid substantially equal to twice the volume trapped between two adjacent gear teeth on one gear and the cylinder walls is delivered to the outlet chamber. The flow meter includes a sensor which is responsive to the movement of the teeth on one gear past a predetermined location swept by the moving gear teeth. The sensor may be of various known designs. For example, the sensor may be an electromagnetic sensor which senses the presence or absence of a gear tooth at the predetermined location. Each time a gear tooth passes the location, an electric pulse is generated. By multiplying the number of pulses over a period of time times the volume of paint delivered through the flow meter each time the gears rotate through an increment equal to the gear tooth spacing, paint flow over the period of time is measured. For certain applications and especially at low flow rates, a higher resolution is desirable than that available from conventional positive displacement flow meters.